The present invention relates to a method for erasing information from a magnetic tape. The tape is divided into at least two physical partitions wherein each physical partition includes a plurality of data tracks carrying recorded data or the like and at least one set of servo tracks carrying position information and dedicated to an area between the data tracks. An apparatus for erasing such information is also disclosed.
More specifically, the invention is applicable to tape drives compatible with QIC standard tape formats, i.e. drives using a 1/4-inch (6.27 mm) magnetic tape width. Quarter-inch cartridge (QIC) drive standards relate to the 10 GByte, 51/4 inch form factor tape drive and the 3 GByte, 31/2 inch form factor tape drive.
The specifications for the 10 GByte standard and for the 3 GByte standard are collected in various documents, for example in QIC-91-41 (QIC-1CF), Oct. 8, 1991, Revision B: "Common Recording Format Specification" and QIC-9142 (QIC-10GB), Oct. 10, 1991, Revision B: "Serial Recorded Magnetic Tape Cartridge for Information Interchange", both for the 10 GByte standard, and QIC-3000, Revision A, Sep. 24, 1991: "Proposed Interchange Standard Serial Recorded Magnetic Tape Cartridge for Information Interchange" for the 3 GByte standard.
As shown in these documents, the tape formats use dedicated servo tracks pre-recorded on the tape by a tape manufacturer. The principle of dedicated servo tracks is disclosed in U.S. Pat. No. 5,008,765. The servo track carries position information for moving a multiple channel head to one of a plurality of predetermined position once the head has been moved proximate to that predetermined position. The use of such servo tracks has effectively avoided read/write errors.
When tape cartridges are worn out and are to be discarded, or if they are to be re-used, the information stored thereon usually must be erased. In particular, if worn out tapes are to be recycled, the information must be deleted with a cheap and efficient method using, preferably, an erase head. Current 1/4-inch tape drive formats in use implement the erase function with a full-width erase head. In this way, the servo tracks are destroyed during the erasing procedure. This is acceptable if the tapes or tape cartridges, respectively, are to be discarded; however, the procedure makes the tapes worthless if it should be re-used for other purposes. This situation often arises when a large number of cartridges has been stored for archival purposes and may thereafter be re-used for other purposes, for example in other offices or departments.
Therefore, a need arises for a method for erasing information from a magnetic tape without destroying position information on the servo track. Relying on over-writing only, as the QIC specifications state, may cause troubles not only if the tapes contain confidential data or proprietary information which must be kept within the company, but also for future applications if the linear recording density may be considerably increased, for example, to 35 GByte. A proposal for such an erasing function is not disclosed by U.S. Pat. No. 5,008,765.
The 10 GByte or 3 GByte drives must also both write and read formerly used tape formats so that efficient data interchange may take place between various models of the QIC drives with the same form factor. Therefore, to ensure full backward functionality of the tape drives, the erase function must be used for these tape formats. Furthermore, the customers are accustomed to this function since an "erase tape command" is available using tape drive software run on most host computers.
It is, therefore, desirable that the same erase function be implemented on the 3 or 10 GByte products. Also, a forward compatibility may be best ensured if the conventional erase function is used for the 10 GByte tapes. This is, in particular, the case if doubling of the cartridge capacity is performed by doubling of the number of tracks (possibly with increased linear density) by using the same tapes having substantially the same magnetic media formulation and using, if possible, the same number of servo tracks as before.
U.S. Pat. No. 4,121,264 discloses a method for recording information signals and control signals in parallel tracks on a magnetic recording medium. The tape has recorded thereon a first main track containing an information signal. The track is recorded in what may be called the forward direction. The tape also includes another main track substantially identical with the first one, but recorded with the tape moving in a reverse direction. A much narrower secondary control track is arranged alongside the first of the main tracks and recorded simultaneously therewith. The distance between the first main track and the associated second control track is selected such that a second secondary control track may be provided therebetween which is associated with the second main information track and is again simultaneously recorded therewith. A special embodiment shows each main track being sub-divided into subtracks having a guard band between them. An erase head is provided capable of erasing both the main information tracks and the corresponding control subtrack by defining an air gap having an overall length equal to the sum of the widths of the control subtrack recorded in the opposite direction and its two guard bands. The erase head is further designed to erase simultaneously the secondary control track that corresponds to both of the subtracks. The respective pole pieces are spaced from one another such that the secondary control track lying between the subtracks and the first secondary control track is not covered by the erasing field of the erase head.